As is known, power actuators must keep down to a minimum the dissipation of power both when on and during switching.
For this reason, for implementing a power actuator, there has been a passage from bipolar transistors (which have low on-dissipation) and from MOS transistors, (which have low dissipation during switching) to hybrid components that combine the advantages of both types.
In addition, power actuators must also have high input impedance and hence be driven with low-voltage pulses. Consequently, the various hybrid solutions that have been proposed (such as, insulated-gate bipolar transistors—IGBTs, MOS-controlled thyristors—MCTs, and emitter-switched thyristors—ESTs), in addition to presenting different levels of compromise between power dissipation when on and during switching, have been designed so as to be able to meet also this requisite and hence are driven by an insulated-gate electrode.
Amongst the hybrid solutions proposed, the most versatile solution is the IGBT one, even though its characteristics do not render it suitable for applications requiring a high blocking voltage (maximum reverse voltage that the device is able to withstand without going into breakdown), which is typically higher than 1200 V. In fact, at higher voltages, the power dissipation in the on state becomes important; on the other hand, in order to increase the blocking voltage, it is necessary to increase the size of the device, With consequent increase in the cost.
In order to overcome the above limitation, structures have been proposed based upon thyristors, which have a smaller forward voltage drop Vf during operation, and driven like MOSFETs, i.e., with a control voltage such as IGBTs. MCTs and ESTs belong to this category.
Both of the solutions have, however, a rather modest reverse-bias safe-operating area (RBSOA) and long turning-off times, so that their use has remained limited to very particular application fields.